This invention relates to equipment useful in earth boring by the rotary system wherein a drill bit is rotated in an earth bore by means of a drill stem. The drill stem comprises a string of tubular members including a plurality of lengths of drill pipe and at the upper end of the pipe string a drive tube. The drive tube is sometimes just another length of pipe, but more often is a non-circular cross-section tube called a kelly. The drive tube is connected to drive means for rotating the drive tube.
Sometimes the drive means is an electric or hydraulic motor geared to the rotating part of a swivel by means of which the drill stem is suspended from the travelling block of a derrick. Such a motor means is called a power swivel.
More often the drive means is a rotary table. A rotary table includes a body having a hole in the middle through which the drive tube extends, torque means to connect the body to the drive tube so that rotation of the body will cause rotation of the drive tube about its axis, and a hydraulic or electric or other motor connected directly or indirectly to the body to rotate the body. Although other arrangements are known, usually the torque means comprises bushing means secured against rotation in the body and having a polygonal aperture through which the drive tube extends, in which case the drive tube is of correlative polygonal cross-section and is known as a kelly. The torque means then may comprise a master bushing received in the hole through the body of the rotary table and a kelly bushing received in the master bushing and slidably engaging the kelly. The kelly bushing is split so that it can be removed from one kelly and put on another whenever desired. Normally, however, during the several weeks during which an earth bore is being made, the kelly bushing remains always connected to one kelly, being prevented from slipping off the ends because the tool joint type connectors at the ends of the kelly are too large to pass through the kelly bushing.
During drilling by the rotary system, the body of the rotary table is turned, rotating the bushings and the kelly and the drill pipe therebelow, and thus rotating the drill bit at the bottom of the hole. Drilling fluid, either aeroform or liquiform, such as air or mud, is pumped down the drill stem, out the bit, and back up the annulus between the earth bore and drill stem. The upper part of the earth bore is usually lined with steel pipe called surface casing, cemented in place in the earth bore. Surmounting the casing and connected thereto by a screw thread connection or a flange connection are one or more steel spools called well heads having side outlets through which access can be had to the annulus, the lowermost spool being connected to and supported by the surface casing and each spool thereabove being connected to the spool therebelow. Each spool may be provided with a conical bowl in which is supported a tapered coupling or hanger on another string of casing of smaller diameter extending farther down in the earth bore, the earth bore getting smaller in diameter as it goes deeper.
During drilling, as soon as the bore reaches a substantial depth, a spool forming the body of a large gate valve, known as a master valve, and one or two additional spools each known as a blow-out preventer (BOP) are added to the top of the stack of well heads. Such a stack may be called the control stack. In case the earth bore penetrates a high pressure formation tending to blow the drill stem and drilling fluid out of the earth bore, movable portions of one of the preventers may be moved to close off the annulus between the drill stem and body of the blowout preventer, the preventer closing tightly about the drill stem so that the tool joints connecting its components, which are of larger diameter than the kelly or drill pipe, cannot pass through the preventer. Or if the drill stem is removed, another preventer or the master valve can be closed to completely block off the whole earth bore.
The stack of well heads and preventers may be ten feet high. The rotary table is mounted on a structure located above the top of the control stack, usually on the floor of a drilling rig erected over the site of the earth bore, such rig carrying also the derrick, drawworks, drilling fluid pumps, and pipe racks.
In the course of drilling, two operations occur regarding handling of the drill pipe. As the bore deepens, the kelly is lowered through the rotary table until the tool joint member or connector at the upper end of the kelly contacts the kelly bushing, preventing further lowering. The drill string is then elevated to bring the upper end of the uppermost length of drill pipe above the rotary table. This causes the kelly bushing to be withdrawn from the master bushing, the kelly bushing having too small an opening for the connector at the lower end of the kelly to pass through the kelly bushing. Slips are then set in the conical bowl of the master bushing to grip the drill pipe and support it in the rotary table. The kelly is unscrewed from the drill pipe, employing tongs and with the assistance of a cat line connected to a winch. The kelly is then put to one side, and another length of drill pipe is connected to the upper end of the drill string, and the string is picked up with elevators connected to the draw works. The slips are removed and the drill string lowered back into the earth bore until only the upper end of the last added length of pipe is above the rotary table. The pipe is then suspended from the table by slips placed in the master bushing, the elevators are released from the pipe and used to pick up the kelly. The kelly is then reconnected to the upper end of the drill string, the string is suspended by the elevators, the slips are removed, the kelly bushing is lowered into the master bushing, and drilling is resumed. This operation is called adding pipe.
Periodically, the drill bit wears out and must be replaced. In such case, the kelly is removed as in the case of adding drill pipe, and then all the drill pipe is pulled out of the earth bore, one or more lengths at a time, and racked at the side of the drill rig. Finally, the last lengths of pipe, usually pipes of greater wall thickness called drill collars, are removed, and lastly the drill bit. A different bit is then substituted and the drill string is put back into the earth bore, one or more lengths at a time. This operation is called "making a trip" or "tripping".
In the course of drilling, the drilling mud is picked up from the mud pit by a slush pump and pumped through a hose to the swivel and down the kelly and the rest of the drill string and the bit and back up the annulus and then through a side outlet in a well head to a flow line going to a shale shaker and then back to the mud pits. Such circulation is discontinued, however, during tripping and when adding pipe. When the kelly and kelly bushing are lifted out of the master bushing, the rig floor is exposed to the open top of the earth bore annulus therebelow. Any momentary pressure rise in the well may cause mud to emerge like a fountain through the rig floor. Or if circulation is maintained while the kelly is pulled up out of the table, upflowing mud in the annulus may splash out of the top of the well head and through the open rotary table out the rig floor. In the case of air drilling, detritus entrained with the air will tend to blow up through the table onto rig personnel performing the tripping or adding pipe operation. Even during regular drilling, mud splashing out of the top of the uppermost well head or bell nipple will make a mess in the neighborhood of the control stack, and in the case of air drilling returning detritus laden air will blast the underside of the rotary table if not controlled.
To prevent such uncontrolled flow of drilling fluid returning from the annulus under the conditions just described, a special well head known as a diverter may be employed to seal off the annulus at the upper end of the control stack. If it is desired to maintain the returning drilling fluid under pressure, as in pressure drilling, a similar device capable of withstanding greater annulus pressure may be employed, such a device being called a rotating blowout preventer. Both diverters and rotating preventers are known under the generic name of drilling heads.
The composite inventions relate to an improved drilling head. Drilling heads are well known in the prior art. Generally a drilling head includes a seal tube rotatably mounted in the spool or body of the head and having a stripper rubber slidably but not-rotatably engaging the kelly and a rotating seal between the seal tube and spool. A split drive bushing engages the kelly and seal tube to rotate the seal tube with the kelly to avoid relative rotation therebetween. Various arrangements are provided for replacing the stripper rubber, the seals, and the bearings, and for lubricating and sealing the bearings, as discussed further in the aforementioned companion application of W. R. Garrett.
An object of the composite inventions is to provide a drilling head made of a multiplicity of components which can be assembled and separated in an improved manner to facilitate installation, operation, and maintenance of the drilling head. Further and more specific object will appear as the description of the composite inventions proceeds.